The invention concerns an UPS (uninterruptible power system) without standby batteries, and more particularly, an UPS in which standby DC power is obtained from a flywheel-driven motor generator set.
Uninterruptible power systems specifically include batteries to provide DC power that keep the UPS operating when utility AC power is interrupted. The short amount of time that DC power must be provided is determined either by the duration of the utility AC power outage or by the length of time necessary to turn on and bring a standby generator up to speed. In the latter case, AC power generated by the standby emergency generator substitutes for the utility AC power.
It is well known that batteries are unreliable and subject to frequent, unpredictable failure. Further, when used to provide standby DC power in an UPS, batteries require constant monitoring and maintenance during their effective lifetimes and replacement when their effective lifetimes expire. For these reasons alone, batteries constitute an undesirable element of an UPS.
Further, most failures of utility AC power are of short duration, lasting only for a few cycles or a few seconds. Longer outages typically last for an extended period and may approach several hours in duration. Most UPS's include a standby emergency generator set that will typically start and attain operating performance levels within a period of ten seconds or less after failure of a utility AC power signal. Thus, the maximum time that an UPS runs on DC power provided by batteries is that 10-second period. In order to meet the load requirements of an UPS, battery systems are typically rated for a minimum of five minutes--4 minutes and 50 seconds longer than necessary.
Accordingly, there is manifold motivation for replacing batteries in an UPS system.